As representative examples of prior screens which project incident images on a viewing space, there are front-directional projection type screens that project incident beams by reflecting them, a rear-directional projection type screens and holographic screens that project incident beams by transmitting them. In reference to drawings, each example will be described as follows.
FIG. 1 is a sectional view of a prior front-direction projection type screen. Like shown in FIG. 1, the prior front-directional projection type screen is designed to view images by forming incident beams (200) projected on a front side of the screen as reflective beams (300), after the incident beams (200) are reflected on the surface of the screen. Commonly, white cloth, film, and an acryl material (100) are used as basic materials of the screen, and there are various treatment methods applied to the surface of the material (100) in order to improve screen characteristics. Specifically, a method of leaving fine scars on the surface of material or coating fine particles such as glass beads (60), or a method of conducting an aluminum coating (80) has been used. Besides, a glass bead protective layer (70) for protecting the glass beads and an adhesive layer (90) is provided as well for attaching the glass beads to the material (100).
However, in case of the front-directional projection type screen, there may be scars owing to external stimulation since the surface of the material is processed like above, and it is difficult to manage the screen cleanly so that a bad angular field is obtained.
FIG. 2 is a sectional field of a prior rear-directional projection type screen having a fresnel lens and a lenticular lens. Like shown in FIG. 2, the rear-directional projection type screen transmits images (200) projected in rear direction, in front direction, so that the user can view the images in front direction.
A simple rear-directional projection type screen can be provided by processing the surface of a transparent film or a transparent acryl(130) in various methods. In detail, there is a method of improving characteristics of the rear-directional projection type screen by forming numerous fine optical lenses, that is, a fresnel lens (110) and a lenticular lens (120), like shown in FIG. 2.
As for an optical lens-type screen with a fresnel and lenticular lens-type screen of FIG. 2, there is a problem of viewing on a side owing to a bad angular field in terms of lens characteristics. Furthermore, it needs fine printing, extruding, and coating technologies, resulting in a complicated fabrication process.
FIG. 3 is a sectional view of a prior holographic screen. Like shown in FIG. 3, the prior holographic screen is configured to view projective beams (400) in front direction by adding directional property to incident beams (200), which are projected at pre-determined angle in rear direction, to the front direction by cubic holograms (50). Such a holographic screen is composed of the cubic holograms (50) interposed between front elements (10) and rear elements (20). The cubic holograms (50) are made with a particular directional property by using short wavelength rays (ex, laser beams), after forming supplementary holograms on the surface of a transmissive material or forming layers with photopolymer or dichromate gelatin, and halogenated silver materials within the transmissive material. Representative examples of the above holographic screen are Holopro Screen of German Pronova corporation and Holo Screen of Japanese DNP corporation.
However, even though the prior holographic screen has a good point of realizing images without disturbing inside/outside visibility, it has a bad angular field on the aspect of characteristics of the cubic holograms (50) assigned with a regular directional property. Moreover, a fabrication method of the prior holographic screen is very complicated and difficult, causing a manufacturing cost of the screen to increase.